1. Field of the Invention
This invention generally relates to a separate type room air conditioner package divided into an indoor unit and an outdoor unit, and more particularly to a method and a device for reducing noises generated at an exhaust port of the indoor unit of the room air conditioner package.
2. Description of the Prior Art
Generally, a separate type room air conditioner package is of the type shown in FIG. 10 of the accompanying drawings and broadly comprises an indoor unit 1 which is installed inside a building, and an outdoor unit 2 which is installed outside the building and connected to the indoor unit by connection pipes 3 to permit a cycle of a heat flow to be effected between the units.
The outdoor unit 2 includes a heat exchanger 4, a compressor 5 and a fan 6 and functions to produce cold air by means of circulation of a refrigerant.
On the other hand, the indoor unit 1 which is installed inside the building is of the general box type as shown in FIGS. 11 and 12 of the accompanying drawings and comprises an intake grid 10 disposed at its lower portion to suck indoor air, a heat exchanger 11 mounted within the unit in the region behind the intake grid 10, a centrifugal fan 12 disposed at the middle portion to compulsorily discharge into an exhaust duct 13 the air cooled by passing through the heat exchanger 11, and an exhaust grid 14 disposed at the upper portion to discharge into the interior of a room the cold air passed through the exhaust duct 13.
In addition, a control panel 15 comprising, for example, a power button, a printed circuit board, etc., for controlling the indoor unit 1 is disposed in the front of the middle portion where the centrifugal fan 12 is located.
In operation of the indoor unit thus constructed, when the indoor unit is switched on through operation of the control panel 15, the centrifugal fan 12 is actuated, so that the indoor air is sucked through the intake grid 10, then passes through the centrifugal fan 12, and is discharged through the exhaust grid 14 into the interior of the room, as shown by the arrows in FIG. 12. At this time, the indoor air of a higher temperature sucked through the intake grid 10 is changed into the cold air having a lower temperature by passing through the heat exchanger 11, so that the air conditioning of the room may be effected. In the indoor unit, noises are generated by flow of the air passing through the unit. The noises take the forms as shown in a noise waveform chart of FIG. 13, a corresponding vibration spectrum of FIG. 14, and noise waveform charts of FIG. 15 illustrating the noises generated at the left, the front and the right sides of the indoor unit. At this time, the dominant frequency band of the noise generated at the indoor unit is the low frequency band less than approximately 600 Hz, and a most violent noise is generated in the region of the exhaust duct. The reason why the noise generated in the region of the exhaust duct is most violent is that while sound pressure in the region is highest, it is difficult to accomplish absorption of the noise of the low frequency band in the exhaust area.